Drive devices socalled universal joints are known intended to drive a rotating movement of two shafts arranged at different relative positions to enable the angular displacement therebetween.
Said devices are typically used in the automotive field to drive rotating movement to the wheels when they are driving and driving wheels at a time, as to steering columns of the motor vehicles where it is not possible to drive the movement by means of a monolithic longitudinal shaft, especially due to the particular geometry of the interior of the vehicle where the various mechanical parts in the steering assembly have to be fitted and to work.
The Axial Displacement Universal Joint provided within the present invention is intended to drive rotating movement between two shafts capable of facing in different directions. To achieve this, one end of said shafts is provided with a first fork having holes intended to receive the ends of the arms of a crosspiece. Said crosspiece hingedly joins said first fork with the ends of a second fork.
The main feature of the present invention is that the second forks of the shafts are mechanically joined to each other by means of an axial displacement device. Said axial displacement device is designed to take up the effects of an external shock which could give rise to interferences on the operation of the mechanical system and even to failures or damages of severe consequences.
In a specific application for steering columns, the use of the universal joint as the one herein described makes possible to advantageously prevent movements from being transmitted from the rack to the steering column of the vehicle thus isolating the columns from the steering assembly.
Another advantage of the present invention is the possibility to change the clearance of the shaft forks which notably facilitates assembly thereof thanks to the play existing therebetween, this allowing the mechanical assembly to be adapted in a more convenient way, always assuring a perfect driving.
More specifically, the axial displacement device of the universal joint of the present invention comprises a first bearing plate that is formed integrally to the second fork of one of the shafts. The axial displacement device also comprises an intermediate plate that is parallel to said first bearing plate. Finally, there is provided a second bearing plate that is parallel thereto.
The first bearing plate of the axial displacement device is provided with guiding and fastening columns. Said columns are formed integrally by one of their ends to the first bearing plate. In turn, these columns are also formed integrally to said second bearing plate by their opposed ends.
The mentioned intermediate plate is provided with through bores adapted to receive said guiding and fastening columns thereacross. Said intermediate plate also has a column formed integrally thereto by an end and, by the other end, to the second fork of the other shaft.
With the disclosed configuration, the relative clearance between said first bearing plate and said intermediate plate defines a displacement between the forks of the respective shafts which provides the above mentioned advantages. Thus, in case of a contingent external stress, the system reacts balancing it by displacing the assembly formed by the columns fixed to the intermediate plate relative to the guiding and fastening columns fixed to the two bearing plates. Hence, there is a relative movement between the forks of the shafts that enables to take up any movement caused by an external agent to the driving system itself, with low sliding load and high twisting stiffness.
The invention also envisages the possibility of providing a flexible protective element that covers the axial displacement device surrounding it so that the mechanical parts are isolated from dust, dirt and other external agents that could affect the dynamic performance of the universal joint. By way of an example, said protective element may be a rubber tube surrounding the device and that, in turn, allows the movement of the elements in an appropriate way.
Additionally, the axial displacement device of the universal joint of the present invention is provided with biasing means tending to keep the clearance between the forks of the respective shafts in the case of an external stress thus allowing taking up of load in the collapse.
Preferably, the first bearing plate of the axial displacement device comprises three cylindrical guiding and fastening columns formed integrally thereto by one of their ends. Their opposed ends are screw fixed to said second bearing plate. The guiding and fastening columns may be hollow bars to reduce the weight of the assembly.
The intermediate plate is provided with friction bushes housed into said through bores to allow the controlled passing of the guiding and fastening columns thereacross and to enhance sliding thereof. Alternatively, the through bores of the intermediate plate have a surface finishing suitable to allow snugly passing of said columns. Thanks to said features, torque transmission with no play and with a very low sliding stress are achieved.
On the other hand, the column formed integrally to the intermediate plate is formed with a cylindrical member fixed thereto passing through a bore of said second bearing plate.
The first bearing plate, the intermediate plate or the second bearing plate may have a quadrilateral or triangular profile with rounded vertexes, even though there is also the possibility of including any appropriate profile.
With a joint as the one herein described it is possible to obtain an effective drive means having a great simplicity and low cost due to the preferred geometries of the plates, as stated above.
Further details and features of the present invention will be apparent from the following description, which refers to the accompanying drawings that schematically represent the preferred details. These details are given by way of example, which refer to a possible case of practical embodiment, but it is not limited to the disclosed details; therefore this description must be considered from a illustrating point of view and without any type of limitations.